In recent years, there has been a growth in number of electronic apparatuses such as portable terminal equipment provided with a touch panel device allowing coordinate data to be input by a push operation with a pen or finger in association with contents displayed.
As the touch panels, analog resistance film type touch panels are most frequently used. Recently, in conjunction with increased demands for light-weight equipment, touch panels formed of two sheets of laminated films, the so-called film-film touch panels are coming to be widely used.
A conventional transparent touch panel will be described below with reference to the accompanying drawings.
FIG. 5 and FIG. 6 are drawings showing the conventional touch panel as mounted on a display unit.
In the drawings, sizes in the direction of thickness are shown expanded for ease of understanding the configuration.
In the conventional touch panel, first transparent conductive film 2 made of indium-tin oxide (hereinafter called “ITO”) or the like is deposited by sputtering or the like on the upper side of first substrate 1 made of a light-transmitting insulating film. Further, second transparent conductive film 4 made of ITO or the like is deposited by sputtering or the like on the under side of second substrate 3 made of a light-transmitting insulating film and disposed to oppose first substrate 1.
First substrate 1 and second substrate 3 are bonded together via outer frame 50 in a picture-frame shape to oppose each other with a predetermined distance kept between first transparent conductive film 2 and second transparent conductive film 4.
Incidentally, outer frame 50 is composed of insulating layers 5A and 5B and adhesive layer 5C as shown in FIG. 5.
Further, within the region of outer frame 50, there are arranged wiring patterns, electrodes, and the like, of which illustration or explanation in detail is omitted.
In the region within outer frame 50, there is formed a region having inner circumferential edge 50L in a rectangular shape as indicated by the dotted line in FIG. 6 and the region within edge 50L allows the touch panel to be used, i.e., it provides a visible area.
At the portion corresponding to the visible area on first transparent conductive film 2, there are disposed small-sized dot spacers 6 (refer to FIG. 5) made of insulating epoxy resin or the like at predetermined intervals. First transparent conductive film 2 and second transparent conductive film 4 are in electrical connection with flexible printed circuit board 7 (hereinafter called FPC) and, thereby, both the films are connected to an external apparatus. On the entire bottom face of first substrate 1 placed at the lower side, adhesive layer 11 for mounting the touch panel on an apparatus is formed. Such a conventional touch panel is mounted by adhesive layer 11 on to liquid crystal display 12 as the mount portion in the apparatus using the touch panel.
Operation of the conventional touch panel will be described below.
When a predetermined menu is displayed on liquid crystal display 12, the user acknowledges the displayed screen via a touch panel. When a desired item is determined, the user makes a push operation on the corresponding position with a pen or finger from above second substrate 3. The push operation allows second substrate 3 to be locally bent down to thereby cause second transparent conductive film 4 corresponding to the pushed position to contact first transparent conductive film 2.
At this time, other portion than the pushed position is kept out of contact by virtue of dot spacers 6 for controlling contact between first transparent conductive film 2 and second transparent conductive film 4.
If predetermined voltages are alternately applied to first transparent conductive film 2 and second transparent conductive film 4, while the films are kept in contact with each other at the particular position by the push operation, a voltage ratio at the contacted position is signaled via FPC 7. Then, based on the signaled data, the pushed position is detected by an external circuit and an operation for the desired item is then performed.
There are disclosures of such conventional touch panels in for example Japanese Patent Non-examined Publication No. H10-222305 and Japanese Patent Non-examined Publication No. H09-251159.
Generally, when a touch panel is mounted on liquid crystal display 12, it is desired that there be no air layer interposed therebetween in order that the displayed picture is prevented from deteriorating due to difference in refractive index of light. The conventional touch panel described in FIG. 5 is configured such that adhesive layer 11 for mounting the same on the external apparatus is provided over the entire bottom face of first substrate 1 and thereby it is stuck on to liquid crystal display 12. However, in a touch panel having outer frame 50, the visible area has a hollowed portion with a thickness corresponding to the thickness in the vertical direction of outer frame 50 in a picture-frame shape. This means that the touch panel substantially has stepped portions at the boundary portions between the visible area and the outer frame. Accordingly, when the surface of the touch panel is pressed down with use of a jig made of rubber or the like to cause adhesive layer 11 to adhere to liquid crystal display 12, air bubbles are liable to be formed in around the boundary portions on account of the existence of the described stepped portions. In the worst case, the air bubbles may be formed or seen in the visible area. Thus, there has been a problem that it is difficult to mount the touch panel in a fully tightly attached state substantially not producing unevenly attached portion.